The invention relates to a procedure and a device for measuring the thickness of a liquid layer.
A toner material is applied to a paper sheet by an electrophotographic printing press and subsequently set in the paper sheet. For this purpose, highly heated rollers are used, that effectively set the toner material with high pressure and heat by embossing, and which grip the paper sheet from below. The counteracting force below the paper sheet is provided by the impression cylinder or an intermediate cylinder. The problem with this customary procedure is that between the heater rollers and the paper sheet stock, particularly the toner material on the stock, adhesive forces are produced which hinder the separation of the heated rollers from the stock. As a remedy, an oil layer is applied by an arrangement of heated rollers, sometime called metering and donor rollers, which ensures a loosening of the heated rollers from the stock following the setting of the toner material.
In order to avoid any adverse effects, it must be ensured that the oil layer thickness always lies within a certain range and that its value is neither too big nor too small. If the oil layer thickness is too small, the adverse effects mentioned above occur, and if the oil layer thickness is too thick, the disadvantages lie in the printing results being oily and/or too shiny. Also, particularly with two-sided printing, a too thick oil layer can result in the soiling of the printing press due to the oil used. It is thus desirable that the oil layer thickness on the heated rollers for setting the paper sheets or on setting rollers or on metering or donor rollers, which the oil layer applies to the heated rollers, be set at a certain value. Up until now, this has been solved by applying an oil layer to the heated setting rollers on the paper sheet in the printing press for test purposes and measuring the oil layer thickness on this paper sheet in the laboratory by a spectroscopic procedure. Apart from this costly testing procedure, an oiling system was established by an operator, who used the delivery device and metering or donor rollers for applying an oil layer based on the oil layer thickness estimated by a test paper sheet and metering and donor rollers. It was expected that an oil layer thickness on the rollers in the order of several hundred nanometers delivered the best printing results.
It is the purpose of this invention to determine the thickness of the liquid layer, in particular that of an oil film on a roller, in a simple manner that would save time and be cost-effective. To achieve this task, a procedure and a device are provided in which the mass of a liquid layer is measured in the printing press by a measuring device, and from the measured mass of the liquid layer thickness, the thickness of the liquid layer on the roller is determined.
In particular, it is advantageous that an addition is provided to a control unit for controlling a delivery unit for delivering liquid on the basis of the liquid thickness calculated from the mass. By the use of a rotary encoder, the position of the roller and the location of the roller at which the measurement of the mass takes place can be determined. Of particular advantage is the use of several measuring devices on various places on the roller, so that the mass of the liquid layer at various places on the roller and consequently a distribution pattern of the liquid can be determined. The distribution pattern provides the solution of the important problem of the various thickness of the liquid layer at various places on the roller. In order not to impair the surface characteristics of the roller, the measuring device is inserted in the rubber sheath of the roller. The measuring device is surrounded by heat protection against the heated roller.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.